The company already donated the "engine" of the container runtime as "containerd" to the Cloud Native Computing Foundation (CNCF) back in 2017. This has become a great success,
Now Docker Inc does the same with "Distribution". Distribution is the successor of Docker Registry and being used in Docker Hub. The main reason, according to the announcement, is to find a wider range of maintainers from different companies and use-cases (not just from Docker Inc).
In the past, Docker Registry was forked and different types of registries were created. Many of the changes and new features were not contributed back to the upstream project. Due to the fact that first Registry and then Distribution were maintained by a company (Docker Inc.) this may have stopped open source developers of contributing code. Now placed into the CNCF Sandbox (evaluation phase), the mindset could change.
This is a very courageous (and positively surprising) act by Docker Inc, as the company continues to struggle making money from their container infrastructure service.